Greetings!

I'm designing an intracardiac electrode sensor that sits on the tip of a catheter and detects electrical potential at the point of contact with the heart wall

It's bipolar and concentric with two rings. The outer ring is around 3 mm in diameter and the inner ring is around 0.8 mm in diameter. The reference electrode is a ring around the catheter located 1 cm away from the tip.

(Not sure if this arrangement is possible)

I'm using the triangular Laplacian approximation, but a little confused to how it works. In order to get the 3 triangular voltages and the central voltage, does that mean I need four electrodes in total at the tip? Three positive electrodes making up the outer ring and the negative electrode as the inner ring?

In other concentric bi-electrode designs, I only see one outer electrode ring. How do they get 3 different voltages from one electrode?